Idaho Const. art. VII, § 4

The property of the United States, except when taxation thereof is authorized by the United States, the state, counties, towns, cities, villages, school districts, and other municipal corporations and public libraries shall be exempt from taxation; provided, however, that unimproved real property owned or held by the department of fish and game may be subject to a fee in lieu of taxes if the fees are authorized by statute but not to exceed the property tax for the property at the time of acquisition by the department of fish and game, unless the tax for that class of property shall have been increased.